Juan P. Díaz

Magnetic anomaly interpretation across the southern central Andes (32°–34°S): The role of the Juan Fernández Ridge in the late Tertiary evolution of the margin

Marine and terrestrial magnetic surveys have been integrated to study the tectonic structure of the convergent margin of Chile between 32°–34°S. Three magnetic domains have been identified: oceanic, continental margin, and subaerial. The oceanic domain has seafloor spreading anomalies (16 (∼37 Ma) to 18 (∼39.5 Ma)) disturbed by anomalies of the Juan Fernandez hot spot chain. In the continental margin, the most prominent fabric are E-W anomalies in the upper slope corresponding to onshore E-W anomalies of large intrusive bodies. Onshore, a N-S lineament of short-wavelength anomalies defines the roots of a Cretaceous volcanic arc. A resembling lineament offshore indicates a submerged older volcanic arc and that continental basement extends to ∼50 km landward of the trench. Absolute Cenozoic plate motion for Nazca and South American plates and dating of the Juan Fernandez chain provide a kinematic model of ridge-continent collision. The reconstruction indicates rapid southward migration of the collision point along ∼1400 km of the margin from 20 to 11 Ma (∼20 cm yr−1). From 11 Ma to present the collison point has migrated at a slower rate along ∼375 km of the margin (3.5 cm yr−1). The predicted location of the subducted portion of the Juan Fernandez chain coincides with the south edge of the southward migrating flat slab segment of the subducted lithosphere and with a cluster of deep earthquakes indicating a causal relationship. In the last ∼10 Myr the ridge has separated a sediment starved trench to the north where subduction erosion may dominate from a sediment filled trench to the south where recent sediment accretion dominates. These observations indicate that subduction of the Juan Fernandez chain plays a major role in arc-forearc tectonics.

Radiative properties of aerosols in Saharan dust outbreaks using ground‐based and satellite data: Applications to radiative forcing

We report on measurements of atmospheric transmission (AT T ) and aerosol optical depth (AOD T ) made at three wavelengths (368, 500, and 778 nm) with a spectroradiometer placed on Tenerife (28.5°N, 16.3°W), Canary Islands. Using the National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) channel 1, we also measured the aerosol optical depth (AOD S ) and albedo over a region of the North Atlantic Ocean extending from 15°-35°N to 12°-25°W. We observe large changes in AT T and AOD T when dust outbreaks pass over this region. Using all these data, we derive the asymmetry factor (g), the single-scattering albedo (ω), and the local mean AOD T and we compute the direct radiative forcing ΔF attributable to mineral dust. The local radiative forcing obtained is over the ocean ΔF = -9.7 W/m 2 and for the land ΔF=-4.5 W/m 2 with an error of±25%. Extending these results to global-scale averages, we obtain values of ΔF of -1.22 W/m 2 over the ocean and -0.57 W/m over land. The forcings attributable to dust are comparable in magnitude to those reported in the literature for anthropogenic sulphate and for biomass burning aerosols.

UV Index Experimental Values During the Years 2000 and 2001 from the Spanish Broadband UV-B Radiometric Network¶

Abstract An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson–Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

Relationship between errors in AVHRR-derived sea surface temperature and the TOMS aerosol index

We investigate the effects of various types of atmospheric aerosols on satellite- derived sea surface temperature (SST) retrievals. The association between aerosol presence identified by the Earth Probe Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) and systematic errors in Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST retrievals is explored. We find a significant increase in systematic PFSST errors in the presence of dust aerosols. Average errors range from 0.34˚C for AI values between 0.5 and 1.0 to 1.74˚C for AI≥1.5. The bias is introduced by the AVHRR channel brightness temperature difference (T4 - T5) which is intended to correct for atmospheric absorption normally due primarily to water vapor. Our study shows that (T4 - T5) is sensitive to the dust aerosols (i.e., TOMS AI values). In contrast, smoke aerosols do not seem to have a significant effect on PFSST errors.

Aerosol radiative forcing efficiency in the UV region over southeastern Mediterranean: VELETA2002 campaign

[i] Atmospheric aerosol effects on spectral global UV irradiance were evaluated during the VELETA2002 field campaign between 8 and 19 July 2002 in southeast Spain. In the first stage, seven UV spectroradiometer and six CIMEL Sun photometer measurements were carried out simultaneously, allowing them to be calibrated and intercompared. The mean ratio obtained for the global irradiance between the spectroradiometers, with regards to a reference instrument, ranges from 0.98 up to 1.04 with standard deviations that oscillate between ±0.01 and ±0.17. In particular, the two spectroradiometers used to obtain the aerosol forcing efficiencies have a ratio of 1.000 ± 0.001. The aerosol optical depth (AOD) obtained with the CIMEL Sun photometers has a standard deviation of lower than ±0.01 for all the channels. Under clear sky conditions, the diurnal aerosol forcing efficiency (ΔDF e ) and fractional diurnal forcing efficiency (ΔFDF e ) was calculated for two Mediterranean stations: Armilla (691 m.a.s.l.) within the boundary layer and Sabinas (2200 m.a.s.l) on the lower limit of the free troposphere and 25 km away from the first station. The ΔDF e values obtained at Armilla range between -2.72 ± 0.45 W m-2/τ 380 and -2.88 ± 0.45 W m-2/τ 440 and between -3.22 ± 0.61 W m-2/τ 380 and -3.40 ± 0.62 W m-2/τ 440 at Sabinas station; the ΔFDF e values range from -8.0 ± 1.4%/τ 380 to -8.6 ± 1.3%/T 440 and -12.0 ± 2.3%/τ 380 to -12.6 ± 2.3%/τ 440 at the two stations, respectively. Also, an experimental aerosol transmittance factor, C T , used to obtain UV satellite derived products was found as a result of the dependence of the global irradiance with the AOD, under cloudless conditions. The average aerosol attenuation factor, η, obtained from the C T , is 6 ± 2% under weakly absorbing aerosols, with a negligible spectral dependence.

Intercomparison of Spectroradiometers for Global and Direct Solar Irradiance in the Visible Range

Abstract This paper presents the results of the analysis of the spectral, global, and direct solar irradiance measurements in the visible range (400–700 nm) that were made in the framework of the first Iberian UV–visible (VIS) instruments intercomparison. The instruments used in this spectral range were four spectroradiometers: three Licor 1800s equipped with different receiver optics and one Optronic 754. For the direct solar irradiance measurements the spectroradiometers were equipped with collimators with different fields of view. Parallel studies have been carried out with the data given by the spectroradiometers with their original calibration file and with the same data that is corrected, following in situ calibration of the instruments using a laboratory reference lamp. To compare the series of spectral data the relative values of mean absolute deviation (MAD) and root-mean-square deviation (rmsd) have been used. The results obtained from the measurements of global irradiance show that the Licor 18...

Simulation of mineral dust effects on UV radiation levels

The role played by aerosols on UV radiative transfer in the atmosphere is very uncertain. This is especially true regarding mineral dust. To determine the sensitivity of the UV levels to the presence of this atmospheric specie, we have simulated the UV irradiance with different vertical distributions of mineral dust. We have used a discrete ordinates radiative transfer model to obtain the UV levels both at sea level and at 3000 m. We have computed the aerosol single-scattering albedo, the phase function, and the asymmetry factor by Mie scattering theory. The background aerosol profiles were taken from WCRP [1986] models, whereas the radiative properties of mineral dust have been calculated from the aerosol size distribution obtained during Saharan dust invasions at Tenerife island (28.5°N, 16.3°W). The values for aerosol optical depth assumed as input for the model calculations are 0.2 (at 550 nm) for clean background aerosols and 0.3 (at 550 nm) for the mineral dust component. From the results we can conclude that the dust vertical size distribution can affect the irradiance ratio F (with Saharan dust)/F (no Saharan dust) by 2-4%. In addition, we observe that to the same total optical depth the diffuse UV levels depend not only on the vertical dust distribution but also on the background aerosol vertical distribution. We have computed differences for the diffuse radiation fluxes of about 5% between a maritime and a continental model to the same mineral dust vertical distribution.

Aerosol Lidar Intercomparison in the Framework of SPALINET—The Spanish Lidar Network: Methodology and Results

A group of eight Spanish lidars was formed in order to extend the European Aerosol Research Lidar Network-Advanced Sustainable Observation System (EARLINET-ASOS) project. This study presents intercomparisons at the hardware and software levels. Results of the system intercomparisons are based on range-square-corrected signals in cases where the lidars viewed the same atmospheres. Comparisons were also made for aerosol backscatter coefficients at 1064 nm (2 systems) and 532 nm (all systems), and for extinction coefficients at 532 nm (2 systems). In total, three field campaigns were carried out between 2006 and 2007. Comparisons were limited to the highest layer found before the free troposphere, i.e., either the atmospheric boundary layer or the aerosol layer just above it. Some groups did not pass the quality assurance criterion on the first attempt. Following modification and improvement to these systems, all systems met the quality criterion. The backscatter algorithm intercomparison consisted of processing lidar signal profiles simulated for two types of atmospheric conditions. Three stages with increasing knowledge of the input parameters were considered. The results showed that all algorithms work well when all inputs are known. They also showed the necessity to perform, when possible, additional measurements to attain better estimation of the lidar ratio, which is the most critical unknown in the elastic lidar inversion.

Radiative forcing under mixed aerosol conditions

[1] The mixture of mineral dust with biomass burning or urban-industrial aerosols presents significant differences in optical properties when compared to those of the individual constituents, leading to different impacts on solar radiation levels. This effect is assessed by estimating the direct radiative forcing (ΔF) of these aerosols from solar flux models using the radiative parameters derived from the Aerosol Robotic Network (AERONET). These data reveal that, in oceanic and vegetative covers (surface albedo (SA) 0.30 are not present in East Asia region. At the bottom of atmosphere (BOA) the maximum ΔF values are associated with the highest AOD levels obtained for the mixture of mineral dust and biomass burning aerosols (-130 ± 44 Wm -2 with AOD = 0.8 ± 0.4 for SA < 0.30).

High-Resolution Future Projections of Temperature and Precipitation in the Canary Islands

AbstractThe complex orography of the Canary Islands favors the creation of microclimates, which cannot be studied using global climate models or regional models with moderate resolution. In this work, WRF is used to perform a dynamic climate regionalization in the archipelago, using the pseudo–global warming technique to compute the initial and boundary conditions from a reanalysis dataset and from results of 14 global climate models. The simulations were performed for three decades, one at present (1995–2004) and two in the future (2045–54 and 2090–99), and for two different greenhouse gas scenarios (RCP4.5 and RCP8.5), defined in phase 5 of the Coupled Model Intercomparison Project. The obtained results, at a 5-km horizontal resolution, show a clear dependence of temperature increase with height and a positive change in diurnal temperature range, which is mainly due to a reduction in soil moisture and a slight decrease in cloud cover. This negative change in soil moisture is mainly a consequence of a de...